Refrigeration device comprising a defrost heater

ABSTRACT

A storage compartment and an evaporator compartment communicating with said storage compartment via a cold air passage and a hot air passage and comprising an evaporator and a defrost heater. Said defrost heater, in a region adjacent to the hot air passage, has a higher heating power density than in a region adjacent to the cold air passage.

The present invention relates to a refrigeration device with a storage compartment and an evaporator compartment which communicates with the storage compartment via a cold air passage and a hot air passage and which contains an evaporator, at which air flowing in from the storage compartment cools off and is subsequently fed back into the storage compartment. These types of refrigeration devices are also known as no-frost appliances.

Hot air flowing from the storage compartment into the evaporator compartment takes moisture with it which tends to precipitate on the evaporator so that a layer of ice builds up on the latter during the operation of the refrigeration device. To avoid any deterioration in the efficiency of the device, this layer of ice must be removed from time to time. A defrost heater is conventionally accommodated in the evaporator compartment for this purpose which defrosts ice from the evaporator and lets it flow away. The defrost water produced collects at the lowest point of the evaporator compartment and from there passes through an outlet into the open air where it can evaporate.

The defrosting process adversely affects the energy efficiency of such a refrigeration device, since the heat energy cannot be used completely for defrosting the ice. So that defrosting can begin at all, the evaporator must namely first be heated up from an operating temperature, which lies below 0° C., to 0° C., and after the end of the defrost process the evaporator must be cooled down again to its operating temperature, before the storage compartment can be cooled again. In addition it is inevitable that heat flows out of the evaporator compartment into the storage compartment during defrosting, and said heat subsequently has to be removed from the latter. Such a heat outflow is all the stronger the higher the temperature in the evaporator compartment during defrosting is.

To minimize the energy consumption during defrosting it is thus desirable to implement in the evaporator compartment as homogeneous as possible a distribution of the temperature which only slightly exceeds the freezing point.

Surprisingly this object can be achieved in a simple manner by the invention by a defrost heater which, in the area adjacent to the hot air passage exhibits a higher heating power density than in an area adjacent to the cold air passage.

The reason for this is that the air flowing through the evaporator compartment unloads the moisture that it carries along with it above all in an area adjoining the hot air passage, so that the layer of ice decreases more rapidly in thickness there than in the area adjoining the cold air passage. The fact that the area of the evaporator adjacent to the hot air passage has a higher power density applied to it than the area adjacent to the cold air passage thaws the ice in the area adjacent to the hot air passage rapidly, so that the layer of ice is essentially broken down over the entire evaporator in the same time. Heating up of areas already defrosted which leads to a large increase in temperature in said areas can be avoided.

The heater preferably takes the form of a plate to allow it to be placed along a main side of the evaporator

Preferably the heater extends below the evaporator, so that air heated up at it can rise through the evaporator.

Preferably the heater has a carrier plate and a heating element arranged on the carrier plate.

The heating element can be attached so as to form a flush fit with the carrier plate material, for example by soldering, in order to guarantee a good heat transfer from the heating element to the plate. Another option to consider for attaching the heating element to the plate might be by latching it on.

To promote heating of the evaporator by radiation as well, the heating element is preferably arranged on a side of the plate facing the evaporator.

It should also be spaced away from the plate over at least part of its length, in order on the one hand not to adversely affect the flow of defrost water which drips from the evaporator onto the plate, on the other hand in order to limit an outflow of heat from the heating element to the plate which would reduce the effectiveness of the heat radiation.

It is also expedient in such a case for the plate to be made from a material such as a metal which efficiently reflects the heat radiation occurring, in order in this way to still direct heat radiation which is radiated from the side facing away from the heating element onto the evaporator.

In accordance with a first embodiment the heating element is more densely arranged in the area of the carrier plate adjacent to the hot air passage than in the area adjacent to the cold air passage. This enables a heating element to be used with a heating power which remains the same along its entire length per unit of length.

Obstruction of the air flowing through the evaporator compartment by the heating element can be kept low if the latter is arranged in serpentines extending in the direction in which the air passes To implement the different distribution of the heating power at least one of the serpentines is then arranged entirely in the area of the carrier plate adjacent to the hot air passage.

In accordance with a second embodiment the heating element in the area adjacent to the hot air passage has a higher heating power per unit of length than in the area adjacent to the cold air passage. This enables a different distribution of the heating power density to be implemented even if the heating element is arranged in the same pattern in both areas.

To keep the structure of the heating element simple, it is preferable in the latter case for the heating element to comprise two sections connected in series, of which one fills the area adjacent to the hot air passage and the other the area adjacent to the cold air passage.

In the two sections the heating element can be arranged in serpentines separated from each other in each case which extend in the direction in which the air passes through the evaporator compartment.

If a defrost water channel is provided on the floor of the evaporator compartment, into which defrost water from the evaporator flows, it can be worthwhile routing a section of the heating element along the defrost water channel in order to ensure that no ice residue prevents the defrost water in the defrost water channel flowing away from the evaporator and a buildup of water freezing again once the defrosting process has finished.

Further features and advantages of the invention emerge from the description of exemplary embodiments given below which refer to the enclosed figures. The figures are as follows:

FIG. 1 a schematic cross-section through an inventive refrigeration device;

FIG. 2 a perspective view of the evaporator housing of the refrigeration device from FIG. 1 with the defrost heater arranged within it;

FIG. 3 an overhead view of the evaporator housing and the evaporator mounted in it in accordance with a second embodiment of the invention; and

FIG. 4 a schematic cross-section through an evaporator housing in accordance with a third embodiment of the invention.

FIG. 1 shows a schematic section through the upper area of an inventive refrigeration device. The refrigeration device has a body 1 and a door 2, which are each implemented in a conventional manner as hollow bodies filled with a heat-insulating foam layer 3. The inside of the carcass 1 is divided up into an evaporator compartment 5 and a storage compartment 6 by a dividing wall 4 which likewise provides heat insulation. The evaporator compartment 5 is largely filled by a housing 7 of an evaporator module in the inner chamber of which an evaporator 8 of a design known per se with vanes running in parallel for to the sectional plane and a coolant line running at right angles to the vanes in serpentines is mounted. A defrost heater 15 is accommodated below the evaporator 8 on the floor of the housing 7. The housing 7 has a hot air passage 9 on its side facing the door 2, through which hot air gets out of the storage compartment 6 into the evaporator compartment 5, and a passage 10 on its side facing the rear wall of the carcass 1 behind which a fan 11 with blades 12 and a motor 13 is accommodated which sucks air out of the housing 7 and pushes it into a cold air passage 14 to the storage compartment 6.

FIG. 2 shows a perspective view of the housing 7 and of the defrost heater 15 mounted within it. The housing 7 has a flat base plate 18 sloping slightly towards the rear, which, with the electrically-operated heating element mounted on it, forms the defrost heater 15. The base plate 18 is made of metal or plastic, with a metallic coating on its upper side, in order to divert the heat radiation radiated downwards from the heating element upwards onto the evaporator 8.

Between the base plate 18 and the rear wall 19 of the housing 7 there is a defrost water drainage channel 20 on the floor of the housing 7, extending over its entire width and inclined towards a discharge opening 21.

The heating element comprises a plurality of serpentines 16, 17 running in the depth direction of the carcass 1. The serpentines 16, 17 are held on the base plate 18 with the aid of elastic clips 22 projecting from the base plate 18. The clips 22 hold the heating element away from the base plate 18, so that defrost water dripping from the evaporator 8 onto the base plate 18 can flow unimpeded from the heating element into the drainage channel 20.

There are alternate short and long serpentines 16 or 17 in the width direction of the base plate 18, with said serpentines only extending in each case below an area of the evaporator 8 adjacent to the hot air passage 9 or below the entire evaporator 8 respectively and thus forming two sections with different heating power densities. Alternatively serpentines can also be provided in more than two different length stages, of which however all start from the side of the evaporator 8 facing the hot air passage 9, in order to heat the evaporator during operation most intensively in its most heavily iced-up area. A straight section 23 of the heating element extends along the drainage channel 20 in order to ensure that no pieces of ice can remain in the latter to prevent the outflow of defrost water.

FIG. 3 shows an overhead view of an evaporator housing 7 with an evaporator 8 and a defrost heater 25 in accordance with a second embodiment of the invention. The shape of the housing 7 with base plate 18 and drainage channel 20 is the same as that described on the basis of FIG. 2, and the evaporator 8 with a coolant tube held in vanes 28 is identical to that described in relation to FIG. 1. The heating element 25 has two sections 26, 27, which differ in their heating output per unit of length. The more powerful section 26 runs below the area of the evaporator adjacent to the hot air passage 9, and the less powerful section 27 below the section of the evaporator adjacent to the rear wall 19 and thus adjacent to the cold air passage. Both sections 26, 27 are laid according to the same pattern, in the form of serpentines 30 extending in the depth direction of the carcass. A serpentine 31 running at right angles across the carcass 1, which belongs to the lower-power section 27, heats the drainage channel 20.

FIG. 4 shows a third embodiment of the invention in cross section. Here the heating element 15 with alternating long and short serpentines 16, 17 of the type shown in FIG. 2 is not held way from the base plate 18 but is connected to the latter for heat conductance by solder 32. In order to prevent condensation water building up on the curves 33 of the serpentines facing towards the drainage channel 20, the short serpentines 16 are bent slightly upwards in this embodiment, so that water can flow through between them and the base plate 18; In the case of the long serpentines 17 the curves extend to over the drainage channel 20, so that here too a free outflow is guaranteed. 

1-12. (canceled)
 13. A refrigeration device with a storage compartment and an evaporator compartment which communicates with the storage compartment via a cold air passage and a hot air passage and which contains an evaporator and a defrost heater, characterized in that the defrost heater has a higher heating power density in an area adjacent to the hot air passage than it does in an area adjacent to the cold air passage. 